This invention relates broadly to the generation of electricity and more specifically to the structure and operation of a hybrid electric generating system.
Hybrid electric generating systems typically include AC and DC sources of electricity for driving an independent single phase or polyphase AC power grid. The DC sources of electricity typically include a battery bank, but may include other sources of DC energy. An inverter couples between the battery bank and the AC power grid to convert the DC electricity from the battery bank into AC electricity. An AC generator more directly couples to the AC power grid. The inverter often includes a battery charging section which occasionally converts power from the AC grid into DC for charging the battery bank.
The AC generator is typically a fossil-fueled device which exhibits a most efficient operating point, where the amount of electricity generated per unit of fuel consumed is greatest. A typical operating procedure for a hybrid electric generating system seeks to operate the AC generator only occasionally and under conditions where it can be operated efficiently. Accordingly, the AC generator will be brought on-line occasionally to drive the electrical load and concurrently charge the battery bank. However, when the battery bank is not due for a recharge and has sufficient charge capacity to drive the electrical load, the AC generator remains off-line and turned off.
Conventional hybrid electric generating systems suffer from an expendability problem. In order to achieve economies of scale, conventional hybrid electric generating systems are designed and built for a maximum capacity, worst case, situation which will not occur for many years. This approach demands the early outlay of an undesirably large amount of resources for which a corresponding income stream will not be available until much later. To make matters worse, this approach typically requires significant on-site construction to produce a one-of-a-kind installation. Moreover, reliability suffers due to a lack of redundancy. The reliability problem is exacerbated for hybrid electric generating systems because such systems are typically used in remote locations not serviced by a public electric power distribution grid which might otherwise serve a backup power source role. Due at least in part to this expandability problem, the usefulness of conventional hybrid electric generating systems is limited.
For example, if a new subdivision of fifty homes is planned for a remote area that is not currently connected to the public electric power distribution grid, a hybrid electric generating system with sufficient capacity to power those fifty homes might be a viable alternative to the expensive option of extending the public electric power distribution grid to that remote area. However, all fifty of the planned homes are not likely to come on-line at the same time, and those resources expended to have the entire fifty-home capacity available when the first homes need electricity are likely to be underutilized for several years. Moreover, no guarantee can be provided that the entire fifty homes will actually be built and occupied, or that a greater number of homes will not be eventually built and occupied. Furthermore, since the hybrid electric generating system might serve as an alternative to, and not a back-up for, or be backed-up by, the public electric power distribution grid, any reliability problem would be a serious concern.
Accordingly, a need exists for an expandable hybrid electric generating system which would allow electric power capacity to grow in an efficient manner with the need for power. Such an expandable hybrid electric generating system would lessen the early outlay of excessive resources, lessen the uncertainties associated with what actual capacity will be needed in the future, better balance the early outlay of resources with income streams, and be reliable.
On the other hand, a practical expandable hybrid electric generating system faces significant obstacles. For example, independent sources of DC electricity should be connected together through DC switchgear for protection and safety, but any significant quantity of such DC switchgear tends to be too expensive for a practical system. Independent hybrid electric generating modules could let DC sources operate independently from one another, but one module could then bear an undesirable share of the electrical load, causing its battery bank to experience an excessive number of charge cycles and an excessive battery replacement cost or its inverter to experience an excessive load and reduced reliability.
Accordingly, it is an advantage of the present invention that an improved expandable hybrid electric generating system and method are provided.
Another advantage is that a hybrid electric generating system with improved reliability is provided.
Another advantage is that an improved expandable hybrid electric generating system using only a small amount of DC switchgear is provided.
Another advantage is that an improved expandable hybrid electric generating system maintaining a plurality of independent DC busses is provided.
Another advantage is that an improved expandable hybrid electric generating system minimizing battery charge cycles is provided.
Another advantage is that an improved expandable hybrid electric generating system using nearly identical power block modules is provided.
Another advantage is that an improved expandable hybrid electric generating system which can be expanded and maintained with only a small amount of skilled labor cost is provided.
Another advantage is that an improved expandable hybrid electric generating system allows nearly identical power blocks to be built and tested at a manufacturing facility and deployed or returned as needed.
The above and other advantages of the present invention are carried out in one form by an expandable hybrid electric power generating system that includes an AC bus, a plurality of power blocks and a controller. The AC bus supplies electrical power to an electrical load. Each power block has a DC energy source coupled to a DC bus of the power block, an inverter coupled to the DC bus of the power block and to the AC bus, and a generator coupled to the AC bus. The controller is in communication with the power blocks. The controller provides instructions to the power blocks causing the power blocks to maintain approximately equal states of the DC busses within the power blocks.